Generally speaking, the plurality of elements (e.g. a gate, a source, a drain, a channel layer, and a pixel electrode) that form an oxide semiconductor thin film transistor are manufactured with a plurality of manufacturing processes, respectively. Specifically, the source and the drain are usually manufactured in the same manufacturing process, whereas the channel layer is manufactured with another manufacturing process. In addition, there is no limitation on the order of the manufacturing processes. For example, the source and the drain may be formed before the channel layer is formed. In addition, when a material layer of the channel layer is formed with a sputtering process, an environmental gas (e.g. oxygen plasma) may form an oxide layer on the surfaces of the source and the drain. Then, when the channel layer covers the source and the drain, oxide layers may exist between the channel layer and the source and between the channel layer and the drain, thus resulting in a higher contact impedance and reducing the device reliability of the oxide semiconductor thin film transistor.
Another manufacture method is to form the channel layer before forming the source and the drain. However, when patterning a conductive layer to form the source and the drain in an etching process, the channel layer located between the source and the drain may be damaged by the etchant, thus reducing the device reliability of the oxide semiconductor thin film transistor.